There is much interest in the general field of the genetic engineering of living organisms. In the genetic engineering of an organism, foreign genetic material, typically a DNA vector constructed so as to express a suitable gene product in the cells of the target organism, is transferred into the genetic material of cells of the organism, through one of a variety of processes. In the past, the transformation techniques have varied widely from organism to organism, and few genetic transformation techniques have been developed which seem applicable to a large number of different organisms in different biological classes or kingdoms. Some of the prior art mechanisms utilized for the insertion of genetic material into living tissues include direct micro-injection; electroporation, a technique in which individual cells are subjected to an electric shock to cause those cells to take up DNA from a surrounding fluid; liposome-mediated transformations, in which DNA or other genetic material is encapsulated in bilipid vesicles which have an affinity to the cell walls of target organisms; and certain specific types of biological vectors or carriers which have the ability to transfect genetic material carried within them into certain specific target organisms, such as the plant transformation vector Agrobacterium tumefaciens and retroviral vectors which are used in animal hosts.
One technique exists which seems applicable to a large range of target organisms. This theory is referred to as particle-mediated genetic transformation. In this technique, the genetic material, be it RNA or DNA, is coated on the small carrier particles. The carrier particles are then physically accelerated into the tissue which is to be transformed. For the process to work, the carrier particles are selected to be small enough so that they may be hurled through the walls and into the interior of cells of the target organism, without causing injury or significant harm to those cells. Several articles have been published describing the techniques and the apparatus utilized in such a particle-mediated transformation technique. Klein et al. "High-Velocity Microprojectiles for Delivering Nucleic Acids into Living Cells," Nature, 327:70-73 (1987); and Sanford, "The Biolistic Process," TIBTECH, 6:299-302 (1988). Sanford and Klein, who are early investigators investigating particle-mediated transformation techniques, utilized a macro-particle to accelerate the small carrier or microparticles. The macroprojectile or macro-particle used by Sanford and Wolfe was literally a bullet fired by a ballistic shell which was, in actual fact, a firearm shell. The use of such extremely high velocity acceleration techniques required a large instrument, with very good shielding and safety interlocks, to prevent inadvertent harm to the experimenters.
A second technique developed for the acceleration of carrier particles carrying biological molecules into target cells for genetic transformations was based on a shock wave created by a high voltage electric spark discharge. This apparatus, described in European published patent application No. 270,356 and in U.S. Pat. No. 5,015,580, involves a pair of spaced electrodes placed in a spark discharge chamber. A high voltage electric discharge is then passed between the electrodes to vaporize a water droplet placed between the electrodes. The spark discharge vaporizes the water droplet creating a shock wave, which accelerates a carrier sheet previously placed on the discharge chamber. The carrier sheet carries thereon the carrier particles, which have the biological genetic materials thereon. The carrier sheet is accelerated toward a retainer screen where the carrier sheet is stopped, the particles are separated from it, and only the carrier particles pass on into the biological tissues. The design for the particle acceleration apparatus as described in these publications was one which involved a desk top, or bench top, apparatus of relatively significant size and complexity and which was relatively immobile.
A smaller particle acceleration apparatus in which the operative portion of the device is hand-held is described in U.S. Pat. No. 5,149,655. The hand-held device permits the acceleration of particles carrying biological molecules into whole living organisms that are larger than can readily be placed onto a bench top unit.